Those "psychological effects" to which Arsène Wenger had referred when considering the significance of this collision between the Premier League's top two may now be afflicting his Arsenal squad rather than bolstering them. Chelsea crossed the capital to win this tie and a place in the League Cup quarter-finals with relative ease. They were more streetwise, more powerful and certainly cannier in key areas, their victory achieved with a goal in each half and plenty to spare. It all seemed ominously comfortable.

Perhaps that was inevitable given the weight of resources at José Mourinho's disposal but Wenger will have departed gripped by familiar frustrations. His personal record remains wretched after his ninth brush with the Portuguese, none of which he has won. If he can block out that horrible reality, then he must wonder if successive home defeats, after Borussia Dortmund's win here last week, could erode the confidence that had been growing in the squad since the second week of the campaign. Liverpool's visit on Saturday is looming large and then follow the return against Borussia, a trip to Manchester United and a visit from high-flying Southampton.

How Wenger must have craved a victory here to pep conviction before that awkward sequence, let alone retain one route to rare silverware. Instead he must now convince a squad that has grown used to near misses that normal recent service is not being resumed. His positive response afterwards, drumming home that there is no need for panic and the mistakes being made are freakish, suggested as much. The problem is the imminent fixture list appears brutal and, for all the clear improvement in this calendar year, these games will put a relatively kind first nine matches in the Premier League in proper context. "You can't go to conclusions too quickly," he said. That may be revisited in a month's time.

Chelsea are taking plenty of heart at the damage they have inflicted on fellow contenders this week. A sixth successive win in October in all competitions appeared assured from the moment César Azpilicueta had poked the visitors ahead midway through the opening period following Carl Jenkinson's horrible error.

Chelsea's had ostensibly been a protest selection. Mourinho was outraged at having to play 48 hours after that thunderous meeting with Manchester City at Stamford Bridge and only Gary Cahill was retained from the starting line-up on Sunday. In reality it was a match-day squad which cost in excess of £250m to assemble, and an XI of seasoned international quality crammed with personnel still with much to prove to the new manager. He has tapped into their hunger before and they responded.

Azpilicueta's reward was similar to that of his compatriot Fernando Torres on Sunday. Chelsea had defended a corner stoutly with Juan Mata calmly sending Samuel Eto'o upfield and the Cameroonian, in turn, slipping a pass to Michael Essien.

The midfielder's pass looped up from Aaron Ramsey's snapped challenge, the ball arcing towards the home penalty area and kicking up from the turf. The retreating Jack Wilshere spotted Jenkinson's intention to nod back towards Lukasz Fabianski and bellowed a warning, pleading with his team-mate to let him collect instead. As with Matija Nastasic on Sunday, this call went unheeded.

The rest was inevitable. Jenkinson's connection was weak and Azpilicueta darted through on the blindside to poke his shot beyond the advancing Pole and in off the far post. Only once before in a seven-year professional career had the right-back scored, for Marseille against Auxerre in his final match for the French club. His expression was still tinged with disbelief as he left the pitch at half-time.

Wenger called out the cavalry, with Mesut Özil on the pitch and Olivier Giroud preparing to replace a wheezing Nicklas Bendtner. The Dane's display provoked grumbling discontent, at best, from the locals. But just as Arsenal considered building up a head of steam, Eto'o hooked a throw-in back into the box, Willian nodded on and Mata took a touch before slamming his finish beyond Fabianski with his right foot. He may feel on the margins but this was a reminder that the Spaniard remains a player of sumptuous talent, vision and finesse.

"The manager is the one who makes the decision but I will always try my best for this club," said Mata. "That's what I'll always try and do. We've played City and Arsenal this week, two of the best teams in Europe, and we've beaten them. That shows we're ready to fight for titles."

Whether Arsenal are remains to be seen but the next month will offer a proper indication of their progress. This seemed like a reality check. It is up to Wenger now to prove it was a blip rather than a portent of things to come.